160 MtK JAMES MURRAY ON 



When the level of Loch Ness is high this forms a mere bay, having the temperature of 

 the rest of the lake, and all the usual lacustrine animals. In summer it is quite cut off 

 from the loch, becomes greatlv heated, and has a stagnant-water fauna distinct from 

 that of the lake. 



The littoral Rotifera in Loch Ness had a very distinct winter maximum develop- 

 ment. They began to be abundant in December, reached the maximum in February, 

 after which there was a steady and great decline. Many species, notably Cathypna 

 ligona, were only seen during the few winter months; others were in the loch all the 

 year round, but increased greatly in numbers in winter. This cycle was traced during 

 two seasons. 



Abyssal Region. 



As I have already pointed out (40), the limited researches made by the Lake Survey 

 have not revealed in the Scottish lochs any peculiar abyssal organisms whatever, except 

 some Rhizopods which Dr Penard regards as peculiar to great lakes (41, 42). 

 Many Rotifers do, however, extend from the littoral region into what would else- 

 where be designated the abyssal region — although that term has no biological significance 

 with us, in the sense in which Forel uses it (14). 



Our knowledge of the vertical range of the littoral Rotifers is based on observations 

 in Loch Ness. There alone have our studies been carried on for a sufficiently long time 

 to justify us in supposing that we have a fairly adequate knowledge of the life of the 

 abyssal region. A few species have been got in the mud of other lochs (i.e. Loch 

 Rannoch, Loch Oich) at moderate depths. In Loch Ness, dredgings have been made 

 with sufficiently fine nets at all depths down to 700 feet, and often enough to lead us 

 to suppose that if Rotifers were abundant we would have found them. Rotifers were 

 abundant at depths of less than 100 feet. Beyond that depth they became rarer as 

 the depth increased, down to 300 feet, after which they dropped out altogether : only 

 on one occasion was a single species, Proales daphnicola, found parasitic upon 

 a worm at 500 feet. Between 250 feet and 300 feet the fine net on several occasions 

 brought up numerous Rotifers, of about twenty species. Dredgings at those depths 

 were unequal, often containing no Rotifers at all. All the Rotifers were of common 

 littoral species. As it is of some interest to know what species are most capable of 

 adapting themselves to varying conditions of light, temperature, pressure, etc., the 

 complete list is given of all the species found at depths exceeding 250 feet : — 



Philodina macrostyla, and the form Monostyla lunaris. 



tubercu/ata. Dinocharis tetraetis. 



Eospkora najas. Metopidia acuminata. 



„ digitata. ,, solidus. 



Diglena uncinata. ,, triptera. 



IHurella tenuior. „ oxysternum. 



DioHchiza tenuior. Coiurus obtusus. 



Euchlanis deflexa. Proales daphnicola. 

 „ lyra. 



